Diagnosis and Treatment of a Morel-Lavallee Lesion in the Lateral Knee With Point-of-Care Ultrasonography

A 14-year-old male presented to the sports medicine clinic for evaluation of right lateral knee pain for three weeks after he took a forceful blow to his right lateral knee during a football game. He reported swelling and bruising and increasing pain since then. Physical exam was significant for an area of fluctuance that was approximately 20 cm in length and 10 cm in width overlying the lateral right knee with associated ecchymosis and decreased sensation. The remainder of the exam was benign. Point-of-care ultrasound showed a large hypoechoic space overlying the lateral knee consistent with a Morel-Lavallee lesion (MLL). Twenty-six milliliters of serosanguinous fluid were aspirated from between the fascial planes, deep to subcutaneous fat but superficial to quadriceps muscles, under ultrasound guidance. The lesion was sclerosed with 1 cc 1% lidocaine without epinephrine and 4 cc dexamethasone 4 mg/mL, and the patient was given compression wrappings to wear for the next four weeks. MLLs are collections of fluid that occur between different planes of subcutaneous tissue following blunt force or shearing trauma. The general mechanism of injury is a closed degloving injury that occurs following damage to the potential space between layers of fascia, dermis, and subcutaneous fat. MLLs are relatively rare lesions and, when identified, are most frequently found in the proximal thigh and associated with serious underlying bony fractures. MLLs are uncommon and difficult to diagnose due to their nonspecific findings of fluctuance, pain, and bruising. This case is unique in its presentation of an isolated MLL in the lateral knee. Early diagnosis and intervention of these lesions prevent further sequelae.